Optical Projector and Image Display Apparatus Using the Same

ABSTRACT

Image disturbance called speckle noise occurs when an image generator has a small effective screen size and a projection lens has a small effective diameter. The present invention is intended to reduce speckle noise. In an optical projector, a viewing angle enlarging ember ( 60 ) for enlarging viewing angle or a scattering member ( 28 ) for scattering image light is disposed near an image display device ( 18 ), such as a liquid crystal panel. Speckle noise can be reduced, suppressing the deterioration of resolution and contrast.

CLAIM OF PRIORITY

The present application claims priority from Japanese applicationsserial no. P2003-421959, filed on Dec. 19, 2003, and serial no.P2004-132481, filed on Apr. 28, 2004, the contents of which are herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

The present invention relates to an image display apparatus capable ofenlarging and displaying an image produced by an image display device asan image generator on a screen by using optical parts including aprojection lens, and an optical projector to be used in combination withthe image display apparatus.

Recently, the so-called pixel-selection type image modulators, such asliquid crystal panels, have become prevalently used instead ofprojection cathode-ray tubes as image generators for projection imagedisplay apparatus. The image modulator, for example, forms an image bymodulating light emitted by a light source, such as a mercury lamp, foreach pixel. The effective screen size of the image modulator is as smallas about 1 inch. The image modulator emits light closer to collimatedlight than that emitted by a projection cathode-ray tube. Therefore, aprojection lens to be incorporated into the image modulator is small andhas a large f-number, which is the ratio of the lens's focal length tothe lens's maximum effective diameter. If the incident light on the lensis nearly collimated light, the speed of the lens is high even if theeffective diameter D of the lens is small.

If the effective screen size of the image generator is small and theeffective diameter D of the projection lens is small, image disturbancegenerally called speckle noise (scintillation) occurs; that is, theprojection image display apparatus employing the image modulator isliable to generate speckle noise. Techniques intended to reduce specklenoise are disclosed in, for example, Japanese Patent Laid-Open Nos.2001-228547 (Reference 1), Hei 7-168282 (Reference 2) and Hei 11-38512(Reference 3).

SUMMARY OF THE INVENTION

Speckle noise occurs when light rays scattered by spatially separateminute diffusing elements interfere with each other at a point. In otherwords, since light emitted from an optional single point on the imagegenerator passes two points on a screen and interfere with each other,the interference becomes more intense and the contrast of speckle noisebecomes higher when the image generator is smaller and the surfacedensity of outgoing light is greater; that is, the smaller the effectivediameter D of the lens becomes, the higher the intensity of theinterference is.

Accordingly, speckle noise can be reduced by increasing the effectivescreen size of the image generator or by using a lens having a largeeffective diameter D, which, however, runs counter to the trend towardusing the image modulator as the image generator. Therefore, measureshave been taken to avoid interference between light rays emitted fromtwo points on the screen or to diffuse the interfering light rays intowhite noise by further diffusion.

A method of avoiding interference between light rays emitted from twopoints on the screen mentioned in Reference 2 forms a lenticular lenssheet included in a rear projection screen of a material not containingany diffusing material, and disposes a diffusing layer at distancelonger than about three times the focal length of the lenticular lensfrom the lenticular lens sheet. Thus the lenticular lens increases thedirections of light rays falling on the diffusing material and causingspeckle noise to avoid interference. Although this method is effectivein eliminating causes of speckle noise, the diffusing layer needs to bedisposed at a distance longer than about three times the focal length ofthe lenticular lens from the lenticular lens sheet. Consequently,resolution is deteriorated greatly, which is a new problem.

A method of converting the interfering light rays into white noise byfurther diffusion mentioned in Reference 3 uses a lenticular lens sheetof three-layer construction formed by sandwiching a transparent middlelayer between first and second diffusing layers. Speckle noise generatedby the first diffusing layer is concealed by the third diffusing layer.This method not only deteriorates resolution but also makes the seconddiffusing layer on the front side look white when external light fallsthereon and decreases contrast in a bright place.

Accordingly it is important to reduce speckle noise that is caused orliable to be caused in an image display apparatus by an image modulatoras an image generator, and a projection lens having a large f-numberincluded in the image display apparatus, suppressing the deteriorationof resolution and contrast.

The present invention has been made in view of the foregoing problemsand it is therefore an object of the present invention to providetechniques capable of satisfactorily suppressing the deterioration ofimage quality when an image modulator is used as an image generator.

The present invention provides, to achieve the object, an image displayapparatus including an image display device and characterized by aviewing angle enlarging film disposed on one side of the image displaydevice or by viewing angle enlarging films disposed on the oppositesides of the image display device, respectively, to correct image lightsuch that viewing angle is enlarged. The viewing angle enlarging filmsmay be viewing angle compensating films having different refractiveindices with the P-wave and the S-wave, namely, birefringent films.

According to the present invention, the image display device is areflection liquid crystal panel or a mirror-reflection opticalmodulator, and the image display device has a roughened reflectingsurface.

The present invention disposes a scattering member in an optical pathbetween the image display device and the projection lens to scatterlight forming an image formed by the image display device. Thescattering member may be disposed near the image display device.

When the image display device is a transmission liquid crystal panel,the scattering member is one of the following members. (1) An exitdustproof glass plate having a haze value greater than that of anentrance dustproof glass plate, (2) a diffusing sheet adhesivelyattached to an exit dustproof glass plate, (3) a diffusing plateinterposed between a transmission liquid crystal panel and an exitpolarizing plate, (4) an exit polarizing plate having a haze valuegreater than that of an entrance polarizing plate and (5) a diffusingsheet adhesively attached to the entrance or the exit surface of adichroic prism for synthesizing red, blue and green images emitted by aplurality of transmission liquid crystal panels.

When the image display device is a reflection liquid crystal panel, oneof or a combination of some of the following members is used. (1) Adustproof glass plate having a haze value greater than that of a generaldustproof glass plate for protecting the reflection liquid crystalpanel, (2) a diffusing sheet adhesively attached to the surface of adustproof glass plate and (3) a diffusing sheet adhesively attached tothe exit or the entrance surface of a beam splitter.

When the image display device is a mirror-reflection optical modulatorhaving a plurality of mirrors, a dust glass plate having a haze valuegreater than that of a general dustproof glass plate as the diffusingmember.

According to the present invention, the deterioration of image qualitydue to, for example, speckle noise or the like can be suppressed when animage modulator is used.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partly cutaway perspective view of an image displayapparatus in a first embodiment according to the present invention;

FIG. 2 is a typical view of an image generator using the transmissionliquid crystal panel included in the image display apparatus shown inFIG. 1;

FIG. 3 is a view of a unit relating to the present invention extractedfrom FIG. 2 showing the image generator according to the presentinvention in the typical view;

FIG. 4 is a view of a second embodiment according to the presentinvention;

FIG. 5 is a view of a third embodiment according to the presentinvention;

FIG. 6 is a view of a fourth embodiment according to the presentinvention;

FIG. 7 is a view of a fifth embodiment according to the presentinvention;

FIG. 8 is a view of a sixth embodiment according to the presentinvention;

FIG. 9 is a typical view of an image generator using a reflection liquidcrystal panel included in an image display apparatus according to thepresent invention in a modification;

FIG. 10 is a typical view of a reflection liquid crystal panel accordingto the present invention;

FIG. 11 is a view of a unit relating with the present inventionextracted from FIG. 9 showing the image generator according to thepresent invention in the typical view;

FIG. 12 is a view of a seventh embodiment according to the presentinvention;

FIG. 13 is a view of an eighth embodiment according to the presentinvention;

FIG. 14 is a view of a ninth embodiment according to the presentinvention; and

FIG. 15 is a typical view of an image generator using amirror-reflection optical modulator according to the present inventionin a modification.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described withreference to the accompanying drawings.

Referring to FIG. 1 showing an image display apparatus in a firstembodiment according to the present invention is a partly cutawayperspective view, an image generator 1 includes a projection cathode-raytube or a reflection or transmission liquid crystal panel, an imagemodulator, such as a mirror reflection optical modulator provided with aplurality of small mirrors, and an illuminating system including a lamp.The image generator 1 displays a small image. The small image isprojected through a projection lens 2 on a rear projection screen 3.Generally, projection distance is long and hence a reflecting mirror 4is disposed in an optical path between the projection lens 2 and therear projection screen 3 to form the image display apparatus in a smalllongitudinal dimension. The image generator 1, the projection lens 2,the rear projection screen 3 and the reflecting mirror 4 are fixedlyheld at predetermined positions, respectively, in a cabinet 5.

Referring to FIG. 2 showing the image generator 1 including atransmission liquid crystal panel according to the present invention ina typical view, light emitted by a lamp 6, namely, a light source, fallson a multilens unit consisting of an entrance multilens array 7 a and anexit multilens array 7 b. The multilens unit makes the distribution ofthe incident light uniform. A beam splitter 8 transmits light beams ofthe same polarization direction. A condenser lens 9 gathers the lightbeams transmitted by the beam splitter 8. A first mirror 10 is used toform the image generator 1 in a small overall size. The first mirror 10reflects the light beams gathered by the condenser lens 9 to change thetraveling direction of the light beams. The light beams reflected by thefirst mirror 10 fall on a first collimator lens 11 for focusing thelight emitted by the lamp 6 on panels, which will be described later. Afirst dichroic mirror 12 transmits red light beams and reflects blue andgreen light beams of the light beams traveled through the firstcollimator lens 11. A second dichroic mirror 13 transmits the blue lightbeam reflected by the first dichroic mirror 12 and reflects the greenlight beam reflected by the first dichroic mirror 12. A relay lens unitincluding a first relay lens 14 a and a second relay lens 14 b isdisposed on a blue optical path for the blue light beam longer than redand green optical paths for the red and the green light beam. A secondmirror 15 disposed between the relay lenses 14 a and 14 b reflects theblue light beam traveled through the second dichroic mirror 13 to changethe direction of the blue light beam. A third mirror 16 a and a fourthmirror 16 b are placed on the red and the blue optical path for the redand the blue light beam, respectively, to change the respectivetraveling directions of the red and the blue light beam such that thered and the blue light beam fall on a red liquid crystal panel 18R and ablue liquid crystal panel 18B, respectively. A second collimator lens 17a, a third collimator lens 17 b and a fourth collimator lens 17 c areplaced in the red, the green and the blue optical path, respectively.The second collimator lens 17 a, the third collimator lens 17 b and thefourth collimator lens 17 c work in cooperation with the firstcollimator lens 11 to focus the light emitted by the lamp 6 on panels,which will be described later. The red, the green and the blue lightbeam reflected by the third mirror 16 a, the second dichroic mirror 13and the fourth mirror 16 b fall on the red liquid crystal panel 18R, thegreen liquid crystal panel 18G and the blue liquid crystal panel 18B,respectively. The red liquid crystal panel 18R for displaying red imagesis combined with a first entrance polarizing plate 19 a and a first exitpolarizing plate 20 a. Similarly, the green liquid crystal panel 18G fordisplaying green images is combined with a second entrance polarizingplate 19 b and a second exit polarizing plate 20 b. The blue liquidcrystal panel 18B for displaying blue images is combined with a thirdentrance polarizing plate 19 c and a third exit polarizing plate 20 c.The light beams traveled through the exit polarizing plates 20 a, 20 band 20 c fall on a dichroic prism 21, namely, optical modulator. Thedichroic prism 21 includes a red light reflecting film 22 and a bluelight reflecting film 23. The red light reflecting film 22 reflects thered light beam passed through the red liquid crystal panel 18R in thedirection of the arrow A toward a projection lens, not shown. The bluelight reflecting film 23 reflects the blue light beam passed through theblue liquid crystal panel 18B in the direction of the arrow A toward theprojection lens. The green light beam passed through the green liquidcrystal panel 18G passes through the red light reflecting film 22 andthe blue light reflecting film 23 and travels in the direction of thearrow A toward the projection lens. Those optical components are housedin the cabinet 24.

FIG. 3 shows a unit included in the image generator 1 in the firstembodiment according to the present invention in a typical view, inwhich parts corresponding to those shown in FIG. 2 are denoted by thesame reference characters. The red, the green and the blue optical pathshown in FIG. 2 are basically the same in construction and function, andhence only one of those optical paths is shown in FIG. 3. The liquidcrystal panel 18 consists of a TFT substrate 25 and an oppositesubstrate 26, and is protected by an entrance dustproof glass plate 27and an exit dustproof glass plate 28. A first viewing angle enlargingfilm 60 is interposed between the liquid crystal panel 18 and theentrance polarizing plate 19. A second viewing angle enlarging film 61is interposed between the liquid crystal panel 18 and the exitpolarizing plate 20. Each of the first viewing angle enlarging film 60and the second viewing angle enlarging film 61 is a viewing angleenlarging film formed, for example, by coating a transparent carrierwith a discotic liquid crystal compound and crosslinking the discoticliquid crystal compound and generally used for enlarging the viewingangle of electron-flood-beam liquid crystal panel or a viewing angleenlarging film equivalent to the same.

A prior art contrast improving film for improving the contrast of aliquid crystal panel is formed by coating a transparent carrier with adiscotic liquid crystal compound and crosslinking the discotic liquidcrystal compound. A technique using the contrast improving film improvesthe contract through the improvement of the orthogonality of the liquidcrystal panel with the S-wave and the P-wave. This technique iseffective in improving contrast, but not effective at all in reducingspeckle noise. Although enlargement of viewing angle is not necessaryfor a liquid crystal panel included in a projection optical system,improvement of contrast is important for such a liquid crystal panel.Therefore, a viewing angle enlarging film developed for the enlargementof viewing angle is used for improving contrast. The viewing angleenlarging film and the contrast improving film are formed from the samematerials. The viewing angle enlarging film and the contrast improvingfilm are different from each other. Whereas the viewing angle enlargingfilm is designed so that contrast inversion may not occur in a wideviewing angle range, the contrast improving film is designed so as toimprove the orthogonality of the liquid crystal panel with the S-waveand the P-wave in a narrow viewing angle range. The viewing angleenlarging film corrects light not to improve contrast, but to enlargeviewing angle. The contrast improving film according to the presentinvention is black and cuts oblique light by a correction plates toprevent light leakage. The viewing angle enlarging film according to thepresent invention is white and corrects image light to make obliquelight pass the correction plates.

When the viewing angle of the liquid crystal panel 18 is enlarged byplacing the viewing angle enlarging films 60 and 61 on the oppositesides of the liquid crystal panel 18 as shown in FIG. 3, the collimationof the light beam transmitted by the liquid crystal panel 18 can beeased. Consequently, the present invention is able to reduce specklenoise that appears on the rear projection screen 3.

A unit included in an image generator in a second embodiment accordingto the present invention will be described with reference to FIG. 4, inwhich parts like or corresponding to those shown in FIG. 3 are denotedby the same reference characters. A liquid crystal panel 18 consists ofa TFT substrate 25 and an opposite substrate 26, and is protected by anentrance dustproof glass plate 27 and an exit dustproof glass plate 28.The exit dustproof glass plate 28 has a haze value greater than that ofthe entrance dustproof glass plate 27, and serves as a scattering memberfor scattering image light. Generally, it is desirable that both theentrance and the exit dustproof glass plate have a high transmittance.However, if it is possible that speckle noise is generated, the exitdustproof glass plate 28 having a high haze value is used. Thus, specklenoise that appears on the rear projection screen 3 can be reduced bygreatly scattering the light transmitted by the liquid crystal panel 18.Speckle noise can be thus reduced by making light beams that causespeckle noise fall on the diffusing member of the rear projection screen3 from irregular directions to make interference between the light beamsdifficult. Although it is possible that speckle noise is generated onthe exit dustproof glass plate 28, this speckle noise scarcely causes atrouble because the exit dustproof glass plate 28 is very close to theimage display part of the liquid crystal panel 18. However, polarizationis disturbed by scattering and, consequently, the contrast of the imageis deteriorated. Therefore, the haze value of the exit dustproof glassplate 28 must be determined such that the reduction of speckle noise andthe deterioration of the contrast are properly balanced. The scatteringof the image light that generates speckle noise to prevent speckle noiselike that done by the present invention is more effective than theimprovement of only the screen on which speckle noise appears directlylike that done by prior art techniques mentioned in References 2 and 3.The exit dustproof glass plate 28 having a high haze value may be formedfrom glass containing a dispersed diffusing material or may be formed bycoating a glass plate with a film of a binder containing a materialhaving a low refractivity by spray coating.

A unit included in an image generator in a third embodiment according tothe present invention will be described with reference to FIG. 5, inwhich parts like or corresponding to those shown in FIG. 4 are denotedby the same reference characters. Generally, a liquid crystal panel 18is a common part and hence, in some cases, it is difficult to form aspecial unit as shown in FIG. 4. In such a case, an exit dustproof glassplate 28 provided with a diffusive sheet 29 adhesively attached to thesurface of the exit dustproof glass plate 28 may be employed. If theliquid crystal panel 18 needs cooling, the diffusive sheet 29 may beformed so as to have a necessary strength, and the diffusive sheet 29may be interposed between the liquid crystal panel 18 and an exitpolarizing plate 20.

A unit included in an image generator in a fourth embodiment accordingto the present invention will be described with reference to FIG. 6, inwhich parts like or corresponding to those shown in FIG. 4 are denotedby the same reference characters. An exit polarizing plate 20 has a hazevalue greater than that of an entrance polarizing plate 19 to use theexit polarizing plate 20 as a scattering member for scattering imagelight. Although a diffusing material contained in a polarizing platedecreases the degree of polarization, the use of the diffusive exitpolarizing plate 20 is effective in reducing the number of componentparts. The exit polarizing plate 20 may be formed by bonding a diffusivesheet to a polarizing plate as mentioned in connection with FIG. 5.Polarized light is not disturbed when such a polarizing plate isdisposed with the polarizing plate facing the entrance side and thediffusive sheet facing the exit side.

A unit included in an image generator in a fifth embodiment according tothe present invention will be described with reference to FIG. 7, inwhich parts like or corresponding to those shown in FIG. 4 are denotedby the same reference characters. A diffusive sheet 30, namely, ascattering member, is attached adhesively to an entrance surface of adichroic prism 21. Separation of a diffusive layer from a liquid crystalpanel 18 deteriorates resolution. Since a diffusive layer is outside twopolarizing plates, the deterioration of contrast due to the disturbanceof polarized light by the scattering effect of a diffusing material doesnot occur. The diffusive sheet 30 may be formed so as to have anecessary strength, and the diffusive sheet 30 may be interposed betweenthe liquid crystal panel 18 and the dichroic prism 21.

A unit included in an image generator in a sixth embodiment according tothe present invention will be described with reference to FIG. 8, inwhich parts like or corresponding to those shown in FIG. 4 are denotedby the same reference characters. A diffusive sheet 31, namely, ascattering member, is adhesively attached to the exit surface of adichroic prism 21. Although the separation of a diffusive layer from aliquid crystal panel deteriorates resolution, the red, the green and theblue light beam can be diffused by the single diffusive sheet 31 becausethe red, the green and the blue light beam pass the exit surface. Thediffusive sheet 31 may be formed so as to have a necessary strength anddisposed apart from the dichroic prism 21.

FIG. 9 is a typical view of an image generator using a reflection liquidcrystal panel included in an image display apparatus according to thepresent invention in a modification of the foregoing image generator 1.Light emitted by a lamp 6, namely, a light source, falls on a multilensunit consisting of an entrance multilens array 7 a and an exit multilensarray 7 b. The multilens unit makes the distribution of the incidentlight uniform. A beam splitter 8 polarizes the light passed themultilens unit in S-polarized light beams. A condenser lens 9 gathersthe S-polarized light beams transmitted by the beam splitter 8. A firstmirror 10 and a second mirror 32 are used to form the image generator 1in a small overall size. The first mirror 10 and the second mirror 32reflect the light beams gathered by the condenser lens 9 to change thetraveling direction of the light beams. The light beams reflected by thefirst mirror 10 and the second mirror 32 fall on a first collimator lens33 for focusing the light emitted by the lamp 6 on panels, which will bedescribed later. A dichroic mirror 34 transmits blue light beams andgreen light beams and reflects red light beams of the light beamstraveled through the first collimator lens 33. A firstwavelength-selective wave plate 35 changes only the blue light beam,namely, S-polarized light beam, transmitted by the dichroic mirror 34into a P-polarized light beam. The green light beam, namely, theS-polarized light beam, and the blue light beam, namely, the P-polarizedlight beam, fall on a first beam splitter prism 36. The first beamsplitter prism 36 reflects the green light beam (S-polarized light beam)toward a green reflection liquid crystal panel 38G for the green lightbeam, and transmits the blue light beam (P-polarized light beam) towarda blue reflection liquid crystal panel 38B for the blue light beam. Thered light beam (S-polarized light beam) reflected by the dichroic mirror34 is reflected again by a second beam splitter prism 37 toward a redreflection liquid crystal panel 38R for the red light beam.

An optical modulator 39 is a third beam splitter prism capable ofsynthesizing optical images provided by the red reflection liquidcrystal panel 38R, the green reflection liquid crystal panel 38G and theblue reflection liquid crystal panel 38B. A half-wave plate 40 isattached to the exit surface of the second beam splitter prism 37. TheS-polarized red light beam is converted into an P-polarized red lightbeam by the second beam splitter prism 37, and the P-polarized red lightbeam is converted into an S-polarized red light beam by the half-waveplate 40. The S-polarized red light beam falls on the third beamsplitter prism 39. The third beam splitter prism 39 reflects theincident red light beam in the direction of the arrow B. The S-polarizedgreen light beam fallen on the green reflection liquid crystal panel 38Gis converted into a P-polarized green light beam by the first beamsplitter prism 36, and the P-polarized green light beam travels throughthe third beam splitter prism 39 in the direction of the arrow B. TheP-polarized blue light beam fallen on the blue reflection liquid crystalpanel 38B is converted into an S-polarized blue light beam, theS-polarized blue light beam is reflected by the first beam splitterprism 36 and is converted into a P-polarized blue light beam by a secondwavelength-selective wave plate 41 that converts only the blue lightbeam from an S-polarized light beam into a P-polarized light beam. TheP-polarized blue light beam travels through the third beam splitterprism 39 in the direction of the arrow B. Those optical components arehoused in the cabinet 24.

FIG. 10 is a typical view of the reflection liquid crystal panel 38employed in the image generator included in the image display apparatusaccording to the present invention. Since the red liquid crystal panel39R, the green liquid crystal panel 38G and the blue reflection liquidcrystal panel 38B are basically the same in construction and function,the reflection liquid crystal panel 38 shown in FIG. 10 is any one ofthe reflection liquid crystal panels 38R, 38G and 38B. Referring to FIG.10, the reflection liquid crystal panel 38 consists of a display unit43, a transparent electrode layer 44, and a dustproof glass plate 45covering the transparent electrode layer 44. The display unit 43consists of a silicon wafer 64, a reflecting mirror 63 having a roughsurface, and a liquid crystal layer 62. Generally, the surface of thereflecting mirror 63 is finished in the smoothest possible surfacebecause the surface having a higher reflectance has a higher reflectingability. However, it is expected that speckle noise is generated, thesurface of the reflecting mirror 63 is roughened. Consequently, specklenoise that appears on the rear projection screen 3 can be reduced bygreatly scattering light emerging from the reflection liquid crystalpanel 38.

FIG. 11 is a view of a unit relating to the present invention extractedfrom FIG. 9 showing the image generator. In FIG. 11, parts like orcorresponding to those shown in FIG. 9 are denoted by the same referencecharacters. The red reflection liquid crystal panel 38R, the greenreflection liquid crystal panel 38G and the blue reflection liquidcrystal panel 38B have display units 43R, 43G and 43B and transparentelectrode layers 44R, 44G and 44B, and dustproof glass plates 45R, 45Gand 45B covering the transparent electrode layers 44S, 44G and 44B,respectively. The dustproof glass plates 45R, 45G and 45B has a hazevalue greater than those of general dustproof glass plates to use thedustproof glass plates 45R, 45G and 45B also as scattering members. Thedustproof glass plate 45R, 45G and 45B having a high haze value may beformed from glass containing a dispersed diffusing material or may beformed by coating a glass plate with a film of a binder containing amaterial having a low refractivity by spray coating.

A seventh embodiment according to the present invention will bedescribed with reference to FIG. 12, in which parts like orcorresponding to those shown in FIG. 11 are denoted by the samereference characters. Generally, a reflection liquid crystal panel 38 isa common part and hence, in some cases, it is difficult to form specialunits as shown in FIGS. 10 and 11. In such a case, diffusive sheets 46R,46G and 46B may be attached adhesively to the surfaces of exit dustproofglass plates 45R, 45G and 45B covering the reflection liquid crystalpanels 38R, 38G and 38B, respectively, as shown in FIG. 12. Thediffusive sheets 46R, 46G and 46B serve as scattering members,respectively. If the reflection liquid crystal panels 38R, 38G and 38Bneed cooling, the diffusive sheets 46R, 46G and 46B may be formed so asto have a necessary strength, and may be formed so as to have anecessary strength, and the diffusive sheet 46R may be interposedbetween the reflection liquid crystal panel 38R and a beam splitterprism 37, and the diffusive sheets 46G and 46B may be interposed betweenthe reflection liquid crystal panel 38G and a beam splitter prism 36 andbetween the reflection liquid crystal panel 38B and the beam splitterprism 36, respectively.

An eighth embodiment according to the present invention will bedescribed with reference to FIG. 13, in which parts like orcorresponding to those shown in FIG. 11 are denoted by the samereference characters. Diffusive sheets 47, namely, scattering members,are disposed on the exit side of beam splitter prisms 36 and 37. Thediffusive sheets 47 disposed behind the beam splitter prisms 36 and 37,which separates image light from unnecessary light, are more effectivethen those shown in FIG. 12 in improving contrast. Since the diffusivesheets 47 are spaced from the reflection liquid crystal panels 38,resolution is deteriorated. Although the diffusive sheets 47 areadhesively attached to the respective exit surfaces of a half-wave plate40 and a second wavelength-selective wave plate 41 in the eighthembodiment, the diffusive sheets 47 may be adhesively attached to therespective entrance surfaces of a half-wave plate 40 and a secondwavelength-selective wave plate 41 for the same effect. The diffusivesheets 47 may be formed so as to have a necessary strength and disposedapart from the half-wave plate 40 and the second wavelength-selectivewave plate 41.

A ninth embodiment according to the present invention will be describedwith reference to FIG. 14, in which parts like or corresponding to thoseshown in FIG. 11 are denoted by the same reference characters. Theeighth embodiment is characterized by a diffusive sheet 48, namely,scattering member, adhesively attached to the entrance surface of athird beam splitter prism 39. Since the diffusive sheet 48 forseparating image light from unnecessary light is disposed below beamsplitter prisms 36 and 37 and the third beam splitter prism 39, thecontrast ability of the ninth embodiment is higher than that of theeighth embodiment shown in FIG. 13. However, resolution is furtherdeteriorated because the diffusive sheet 48 is spaced a long distanceapart from the reflection liquid crystal panels 38.

The image display apparatuses in the preferred embodiments shown inFIGS. 10 to 14 have both advantages and disadvantages in contrastability, resolution and the number of parts. Therefore, those imagedisplay apparatuses may be selectively used taking into considerationthe total ability of the image display apparatuses.

FIG. 15 is a typical view of an image generator using amirror-reflection optical modulator according to the present inventionin a modification. Light emitted by a lamp 6 is uniformed by a lightpipe 49. Light emerging from the light pipe 49 is periodically separatedinto red, green and blue light beams by a color wheel 50. Then, theright, the green and the blue light beam travel through a condenser lens51, and are reflected toward a mirror-reflection optical modulator 53 bya mirror 52 used for forming an image generator 1 in a small size. Themirror-reflection optical modulator 53 is protected by a dustproof glassplate 54. A diffusive sheet 55 is adhesively attached to the exitsurface of the dustproof glass plate 54. Those optical components arehoused in a cabinet 56. This image generator 1 is characterized in thatthe dustproof glass plate 54, the diffusive sheet 55 or the combinationof the dustproof glass plate 54 and the diffusive sheet 55 is used as ascattering member. Since the mirror-reflection optical modulator 53 doesnot deal with polarized light, the diffusive sheet 55 may be disposed atany position on the exit side of the mirror-reflection optical modulator53. It is the simplest method of using the diffusive sheet 55 toadhesively attach the diffusive sheet 55 to the exit surface of thedustproof glass plate 54. Since all the pixels of the mirror-reflectionoptical modulator 53 are minute mirrors, not shown, the surfaces of allthe minute mirrors may be roughened. The mirror-reflection opticalmodulator 53 having the minute mirrors having roughened surfaces is aspecial type and there are many difficulties in manufacturing such aspecial mirror-reflection optical modulator. However, since such amirror-reflection optical modulator causes secondary scatteringscarcely, the deterioration of contrast is limited to the least extentand resolution is not deteriorated.

Although the image display devices provided respectively with thetransmission liquid crystal panels, the reflection liquid crystal panelsand the mirror-reflection optical modulator have been described, thesame principle of speckle noise reduction applies to other image displaydevices. Therefore, it goes without saying that the present invention isapplicable to image display devices other than those specificallydescribed herein.

1. An image display apparatus comprising: a light source; an imagedisplay device capable of forming an image by modulating light emittedby the light source; a projection lens for projecting the image formedby the image display device on a screen in an enlarged image; and aviewing angle enlarging member disposed on either of entrance and exitsides of the image display device or on both the entrance and the exitside of the image display device; wherein the viewing angle enlargingmember corrects image light representing the image formed by the imagedisplay device such that viewing angle is enlarged.
 2. The image displayapparatus according to claim 1, wherein viewing angle enlarging memberis a film having different refractive indices with the S-wave and theP-wave.
 3. An optical projector comprising: an image display device; anoptical element for projecting an image formed by the image displaydevice in an enlarged image; and a viewing angle enlarging memberdisposed near the image display device to enlarge viewing angle.
 4. Animage display apparatus comprising: an image display device; an opticalelement for projecting an image formed by the image display device in anenlarged image; a rear projection screen on which the optical elementprojects the enlarged image; and a viewing angle enlarging memberdisposed near the image display device to reduce speckle noise byenlarging viewing angle.